A sucker rod is a steel

Steel

Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 rod, typically between 25 and 30 feet (7 to 9 meters) in length, and threaded

Screw thread

A screw thread, often shortened to thread, is a helical structure used to convert between rotational and linear movement or force. A screw thread is a ridge wrapped around a cylinder or cone in the form of a helix, with the former being called a straight thread and the latter called a tapered thread...

 at both ends, used in the oil industry to join together the surface

Surface

In mathematics, specifically in topology, a surface is a two-dimensional topological manifold. The most familiar examples are those that arise as the boundaries of solid objects in ordinary three-dimensional Euclidean space R3 — for example, the surface of a ball...

 and downhole components of a reciprocating piston pump installed in an oil well. The pumpjack

Pumpjack

A pumpjack is the overground drive for a reciprocating piston pump in an oil well....

is the visible above-ground drive for the well pump, and is connected to the downhole pump at the bottom of the well by a series of interconnected sucker rods.

Working
The surface unit transfers energy for pumping the well from prime-mover to sucker rod string. In doing this, it must change the rotary motion of prime-mover to reciprocating motion of sucker rod. And it must reduce the speed of prime-mover to suitable pumping speed. Speed reduction is accomplished at gear reducer. And rotary motion of crank shaft is converted to oscillatory motion by means of walking beam. The crank arm is connected to the walking beam by means of pitman arm. Walking beam is supported by Samson post and saddle bearing. The horse head and bridle are used to ensure that pull on the sucker rod string is vertical all times so that no bearing movement is applied to that part of sucker rod string above stuffing box. The polished rod and stuffing box combination is used to maintain a good liquid seal at the surface.